Extraction of oil from oil-bearing materials

ABSTRACT

The invention relates to the extraction of oil from seeds and other oil-bearing materials. The oil-bearing material is first treated with a polar solvent such as isopropyl alcohol in aqueous solution and then a second solvent which has a lower polarity and which may be hexane is passed through the once-treated material. The treatment with the first solvent facilitates the passage of the second solvent through the material and hence the extraction of the oil from the material. Water may be added to the extract recovered from the treatment with the second solvent, to aid separation of the oil from other constituents of the material.

United States Patent [151 3,696,133 Lloyd et a]. [451 Oct. 3, 1972 [541EXTRACTION OF OIL FROM OIL- 3,113,954 12/1963 Upton. ..260/4l2.8

BEARING MATERIALS [72] Inventors: Anthony Michael Lloyd, Walkington;David George Alexander, Kirkella, both of England [73] Assignee: RoseDowns & Thompson Limited,

Kingston-upon-Hull, Yorkshire, England [22] Filed: April 13, 1970 [21]Appl. No.: 28,149

[52] US. Cl ..260/412.8

[51] Int. Cl. ..Cllb 1/10 [58] Field of Search ..260/412.8

[56] References Cited I UNITED STATES PATENTS 2,726,253 12/1955 Gastrocket al. ..260/4l2.8

2,781,336 2/1957 Zenczak ..260/412.8

Primary Examiner-Lewis Gotts Assistant Examiner-Johnnie R. BrownAtt0rneyl-lolcombe, Wetherill & Brisebois ABSTRACT The invention relatesto the extraction of oil from seeds and other oil-bearing materials. Theoil-bearing material is first treated with a polar solvent such asisopropyl alcohol in aqueous solution and then a second solvent whichhas a lower polarity and which may be hexane is passed through theonce-treated material. The treatment with the first solvent facilitatesthe passage of the second solvent through the material and hence theextraction of the oil from the material. Water may be added to theextract recovered from the treatment with the second solvent, to aidseparation of the oil from other constituents of the material.

16 Claims, No Drawings This invention relates to the extraction of oilfrom oil bearing materials, particularly of animal or vegetablederivation.

Oil bearing vegetable seeds normally consist of oil, water, proteincarbohydrates and fiber. Animal material is largely oil, protein, waterand minor amounts of carbohydrates.

In conventional processing, the oil is removed by cooking the animal orvegetable material and then extracting the 'oil by applying pressure orby the use of solvents. The material from which the oil has been removedis known as meal and is commercially valuable, chiefly as an animal foodstuff. The value of the meal as food stuff is, in many cases, limited bythe presence of small amounts of toxic impurities, for example gossypolin cottonseed, atlatoxin in groundnut meal and trypsin inhibitor in soyabean meal. The toxic nature of these impurities is, reduced by cookingthe seed, often in the presence of added moisture. Cooking also aids thesubsequent extraction of the oil in conventional processes butunfortunately renders the valuable protein in the meal less readilydigestable when used as a food stuff.

Various proposals have been made to produce an improved quality of mealby extracting the raw material or the meal with a variety of solvents,or solvent mixtures. it has been proposed in British Pat. specificationNo. 905607 for example to solvent extract material containing oil orfats with at least percent water, by the use of a water miscible solventor solvent mixture and possibly a further solvent which may be miscibleor immiscible with the first solvent. The material is treated with amixture of the water-miscible solvent and water to remove theundesirable constituents; then the resulting solids are treated withcomparatively water free solvent, which may be the same as the firstsolvent used, or may be another solvent which is miscible or immisciblewith the first solvent. The extract, after separation from the meal, isfed back to the previous stage until it reaches the first stage fromwhich the extraction liquor is removed. The extraction liquor is thenallowed to separate into two phases, one phase containing substantiallyall the water and the other phase substantially all the fat.

In practice, this separation of the two liquid layers can be difficultto carry out. For effective separation the specific gravities of thelayers of water containing solvent and oil containing solvent must beappreciably different, and this imposes limitations on the process, inparticular in the choice of solvents. The separationof the two layersmay be further complicated by the occurrence of emulsifying agents inthe extract. When solvent mixtures are employed on a commercial scalethe task of recovering the solvents from the meal, the oil, and from thewaste water and then removing the dissolved water from the recoveredsolvent can be costly. Furthermore, the process disclosed in BritishPat. specification No. 905607 has the disadvantage that a mechanicalseparator is required for each stage of the process, since in each stagethe solvent and the solid material must move co-currently; also, themechanical separation of oil seeds from the water containing solvents isdifficult. The liquid is retained tenaciously and,

in the screw press type of machine described in the specification,excessive amounts of fine material are produced in the press liquors,giving rise to a third semi-solid layer to be separated from the twoliquid layers mentioned in the specification.

The present invention resides in a process for the extraction of oilfrom oil-bearing materials, in which the material is first treated witha solution in water of a polar solvent which is at least partiallymiscible with water, and the once treated material is extracted with asecond solvent of lower polarity in which the oil is soluble but whichis substantially immiscible with water, an extract being obtained whichis predominantly the second solvent and contains oil, but which alsocontains an amount of the polar solvent water and undesirableconstituents. Preferably the extract is treated by adding water, whenmuch of the polar solvent, water and undesirable matter separate as anaqueous layer which can be removed from the oil-containing layer.

The polar solvent may be added in an amount such that all is absorbed bythe oil-bearing material. It is however preferred to use sufficient ofpolar solvent and water to give a separate extract which is separatedfrom the material, thus removing some of the undesirable constituents,before the material, together with such of the first solvent that isabsorbed, passes to the extraction stage using the second solvent.

It is known that if uncooked comminuted oil seed is treated with anon-polar solvent and agitated vigorously, the oil is extracted and itis very difficult to separate the finely divided extracted seed from theoil containing solvent.

Surprisingly, we have found that, if the material is treated first witha polar solvent and then with a nonpolar solvent the material becomesparticulate and separation from the solvents is easier. The polarsolvent required may be used to give a preliminary extraction, in whichcase, a first extract containing non-oil impurities is removed, or maybe used in such quantity that it is all absorbed by the seed, which isthen extracted with the non-polar second solvent. The increased easewith which the solvent separates from the seed in the main extraction issuch that in favorable cases the extraction with the second solvent maybe carried out in a rotary solvent percolation extraction equipmentknown as a Rotocel, as described in US. Pat. No. 2840459.

Instead of a Rotocel, which is a multistage percolation extractor, it ispreferred that extraction shall be carried out in a device where thesolvent and solid material move continuously counter current to oneanother, separation of the solid and liquid being by gravitationalmeans, so making it possible to obtain multiple extraction stageswithout the expense of using filters and centrifuges between eachextraction stage. This is particularly desirable in the case of mixturesof solvents with solids which are compressible and therefore not readilyseparated from liquids by conventional means.

The first polar solvent may be used in such small amounts as to be allabsorbed by the oil bearing material, which then passes into theextractor where it is treated in counter current flow with the non-polarsecond solvent; alternatively, the first polar solvent may be used inlarger quantity in a first extractor where the solvent moves countercurrent to the flow of material so giving a multi-stage extraction withthe first solvent. An extract is recovered from the first extractor andthe solid from the first extractor is separated from the freely drainingfirst solvent before passing to a second extractor where it is treatedin counter current flow with the second non-polar solvent which extractsthe oil in a multi-stage extraction process.

It is preferred to employ for the treatment with the non-polar solvent,or for each extraction in the case where counter-current flow isemployed in both stages, a mixer separator as described for example inBritish Pat. specification No. I 184345. The oil-bearing material in thelatter case is thus first continuously treated in a first mixerseparator in which the material and the aqueous polar solvent passcounter-current, and thereafter the material from that mixer separatoris continuously fed to, and treated in, a second mixer separator inwhich the once-treated material with absorbed aqueous polar solution ispassed counter-current with the second solvent.

After the second extraction the second non-polar solvent together withthe dissolved oil contains a small amount of the first polar solventtogether with non-oil impurities. A preliminary purification of thisoil-containing solution is achieved by agitating the mixture with asmall amount of water; the mixture then readily separates into twolayers, a non-polar solvent layer containing the oil in solution and apolar solvent layer containing the water and impurities carried into theoil with the first solvent. The same separation is achieved without theaddition of water, if the first solvent already contains much water. Themeal from the second extraction contains solvent, but this is nearly allthe second non-polar solvent, the first polar solvent having beenremoved by the second extraction process. This second solvent beingnon-polar is weakly absorbed by the meal and so desolventisation iscomparatively easy.

The first or polar solvent can be an alcohol or ketone, the preferredsolvent being a mixture of isopropyl alcohol and water correspondingmore or less to the azeotrope recovered by distillation of a mixture ofwater and isopropyl alcohol. The second non-polar solvent may be anhydrocarbon or chlorinated hydrocarbon and is preferably a commerciallyavailablc petroleum fraction which is low in aromatic hydrocarboncontent and which consists largely of hexane or heptane.

This combination of solvents offers considerable advantages. Bothsolvents are relatively cheap and nontoxic and are, therefore, safe touse in the processing of food stuffs. A further advantage is that themixture of hexane, isopropyl alcohol and water forms a ternary azeotropewith a lower boiling point than any of its constituents:desolventisation of the meal is thus aided. In the presence of steam theternary azeotrope is vaporized for so long as both hexane and isopropylalcohol are present together in the meal. When all the isopropyl alcoholhas been removed in this way, then any residual hexane may be evaporatedat its boiling point, as is well known in the art.

EXAMPLE A sample of very old cottonseed which had deteriorated badly instorage was rolled to break down the cellular structure and extracted.The extractor was a vet .ical glass column fitted with an axial shaftrotating at 145 rpm. and having agitators at 6 inch centers. The solventused for extraction passed up the column through the seed bed and wasthen recirculated to the base of the column via a pump and a heatexchanger. After 20 minutes extraction the solvent was run off from thebase of the column until the stream of drained miscella slowed to anegligible flow rate. More solvent was then added (Run 2) and theextraction procedure repeated.

Test 1.

In this test, the seed was wetted with its own weight of isopropylalcohol containing I3 percent water, all the solvent being absorbed bythe seed, allowed to stand for 20 minutes and extracted as describedabove four times with hexane at 50 C. The following are the amounts ofliquid recovered on each run expressed as a percentage of the amount ofhexane added in the run.

Recovery Run I Run 2 123 Run 3 I03 Run 4 I08 Recovery (isopropylalcohol) 83 I02 75 I I8 Recovery (hexane) I23 I07 I07 Autu- Run Test 3.

To give a comparison, the seed was extracted at 50 C with hexane alone,i.e. without a prior treatment with isopropyl alcohol. As before, thesolvent used in Run 1 was increased by the weight of seed, the addedamount being disregarded for the calculation of recovery Recovery Run 155 2 98 3 86 4 95 These recovery values show very clearly that whereasthe hexane-treated seed in Test 3 drained badly, much of the solventbeing retained by the seed, addition of polar solvent prior to hexaneextraction gave a granular seed mass which drained well in Tests 1 and2. Oil extraction was substantially complete in each case, but in Test 2considerable amounts of gums and sugars were removed with the isopropylalcohol to give a lighter colored meal. This is illustrated by thefollowing data on the oil recovered by evaporating the hexane solutions,the data illustrating also the poor quality of the oil resulting fromthe degraded state of the seed:

Test 3 Test 1 Test 2 Free fatty. 9.9 9.9 3.5 acid Colour Too dark to l6Y21R Too dark to (Lovibond) measure measure W cell) A modified WessonLoss procedure illustrates the improvement in oil quality which therefining could give 1 Test 3 Test 1 Test 2 Refining loss 2l% 6% Colourof 3OY l7R l2Y 1.5R 0.7Y 0.7R refined oil (16" Lovibond cell) Theseresults show that by suitable choice of extraction procedure using firsta polar solvent for example isopropyl alcohol containing water andsecondly a nonpolar solvent for example commercial hexane, thepercolation extraction of uncooked seed may be facilitated and the oilso obtained may be refined to a better standard than is obtained whenusing simple extraction with commercial hexane.

In Tests 1 and 2, the hexane extract is subsequently treated by theaddition of water, when the extract setties into two layers a hexanelayer containing the extracted oil and an aqueous layer containing polarsolvent and undesirable constituents of the seed. The separated hexanelayer is then treated for solvent recovery and further oil purification.

We claim:

1. In a process for the extraction of oil from an oilbearing vegetablematerial in which said material is treated with an aqueous solution of apolar solvent which is at least partially miscible with water; theimprovement comprising the following steps of a. extracting the treatedmaterial containing at least some of said polar solvent with a secondsolvent which is of lower polarity than said polar solvent, in which theoil is soluble, and which is substantially immiscible with water;

. thereby obtaining an extract of the oil dissolved in said secondsolvent, which extract is free of said vegetable material but which alsocontains an amount of said polar solvent and water;

c. separating out said second solvent and dissolved oil; and

recovering the oil from the solution of said second solvent.

2. In a process for the extraction of oil from an oilbearing vegetablematerial in which the material is treated with an aqueous solution of apolar solvent which is at least partially miscible with water; theimprovement comprising the further steps of a. extracting the treatedmaterial containing at least some of the polar solvent with a secondsolvent which is of lower polarity than said polar solvent, in which theoil is soluble, and which is substantially immiscible with water;

b. thereby obtaining an extract of the oil dissolved in said secondsolvent which extract is free of said vegetable material but which alsocontains an amount of said polar solvent, water and undesirableconstituents of said vegetable material;

c. if necessary, adding further water to said extract;

d. allowing said extract to separate into two layers of which a firstcontains said second solvent and dissolved oil and a second containssaid polar solvent, water, and said undesirable constituents;

e. separating said first layer; and

f. recovering the oil from said first layer.

3. A process for the extraction of oil according to claim 2 in which allthe polar solvent added is absorbed by the oil-bearing material, therebeing no percolation.

4. A process for the extraction of oil according to claim 1 in which thepolar solvent is caused to percolate through the material to extractundesirable constituents prior to extraction of the material with thesecond solvent.

5. A process for the extraction of oil according to claim 1 in which thepolar solvent is an alcohol or a ketone.

6. A process for the extraction of oil according to claim 5 in which thepolar solvent is isopropyl alcohol.

7. A process for the extraction of oil according to claim 6 in which thepolar solvent is the azeotrope recovered by the distillation of amixture of water and isopropyl alcohol.

8. A process for the extraction of oil according to claim 1 in which thesecond solvent is an hydrocarbon or chlorinated hydrocarbon.

9. A process for the extraction of oil according to claim 8 in which thesecond solvent is a commercially available petroleum fraction which islow in aromatic hydrocarbon content.

10. A process for the extraction of oil according to claim 9 in whichthe second solvent is hexane.

11. A process for the extraction of oil according to claim 1 in whichthe material after treatment with the polar solvent is treated incounter-current flow with the second solvent.

12. A process for the extraction of oil according to claim 11 in whichthe treatment with the second solvent is effected is a plurality ofcounter-flow stages.

13. A process for the extraction of oil according to claim 11 in whichthe extraction with at least the second solvent is performedcontinuously in a mixer separator.

14. A process for the extraction of oil according to claim 11 in whichthe material is first continuously treated with the polar solvent in afirst mixer separator in which the material and the aqueous polarsolvent pass counter-current, and thereafter the material from thatfirst mixer separator is continuously fed to, and treated in, a secondmixer separator in which the oncetreated material with absorbed aqueouspolar solution is passed counter-current with the second solvent.

15. Process as claimed in claim 1 in which said vegetable material is aseed material.

16. Process as claimed in claim 15 in which said polar solvent is amixture of water and at least one material selected from the groupconsisting of alcohols and ketones.

2. In a process for the extraction of oil from an oil-bearing vegetable material in which the material is treated with an aqueous solution of a polar solvent which is at least partially miscible with water; the improvement comprising the further steps of a. extracting the treated material containing at least some of the polar solvent with a second solvent which is of lower polarity than said polar solvent, in which the oil is soluble, and which is substantially immiscible with water; b. thereby obtaining an extract of the oil dissolved in said second solvent which extract is free of said vegetable material but which also contains an amount of said polar solvent, water and undesirable constituents of said vegetable material; c. if necessary, adding further water to said extract; d. allowing said extract to separate into two layers of which a first contains said second solvent and dissolved oil and a second contains said polar solvent, water, and said undesirable constituents; e. separating said first layer; and f. recovering the oil from said first layer.
 3. A process for the extraction of oil according to claim 2 in which all the polar solvent added is absorbed by the oil-bearing material, there being no percolation.
 4. A process for the extraction of oil according to claim 1 in which the polar solvent is caused to percolate through the material to extract undesirable constituents prior to extraction of the material with the second solvent.
 5. A process for the extraction of oil according to claim 1 in which the polar solvent is an alcohol or a ketone.
 6. A process for the extraction of oil according to claim 5 in which the polar solvent is isopropyl alcohol.
 7. A process for the extraction of oil according to claim 6 in which the polar solvent is the azeotrope recovered by the distillation of a mixture of water and isopropyl alcohol.
 8. A process for the extraction of oil according to claim 1 in which the second solvent is an hydrocarbon or chlorinated hydrocarbon.
 9. A process for the extraction of oil according to claim 8 in which the second solvent is a commercially available petroleum fraction which is low in aromatic hydrocarbon content.
 10. A process for the extraction of oil according to claim 9 in which the second solvent is hexane.
 11. A process for the extraction of oil according to claim 1 in which the material after treatment with the polar solvent is treated in counter-current flow with the second solvent.
 12. A process for the extraction of oil according to claim 11 in which the treatment with the second solvent is effected is a plurality of counter-flow stages.
 13. A process for the extraction of oil according to claim 11 in which the extraction with at least the second solvent is performed continuously in a mixer separator.
 14. A process for the extraction of oil according to claim 11 in which the material is first continuously treated with the polar solvent in a first mixer separator in which the material and the aqueous polar solvent pass counter-current, and thereafter the material from that first mixer separator is continuously fed to, and treated in, a second mixer separator in which the once-treated material with absorbed aqueous polar solution is passed counter-current with the second solvent.
 15. PRocess as claimed in claim 1 in which said vegetable material is a seed material.
 16. Process as claimed in claim 15 in which said polar solvent is a mixture of water and at least one material selected from the group consisting of alcohols and ketones. 